A linear planar-magnetron, of the type generally used in in-line sputtering machines, usually has an elongated rectangular cathode body having target material attached to a surface of the body. The cathode body includes a target-supporting member or target-backing plate for supporting a target material to be sputtered. The target backing plate generally forms one surface of a box-shaped enclosure through which water is be passed for cooling the planar-magnetron during sputtering.
The target material is positioned over a magnet-array located within the enclosure. The magnet-array usually comprises three spaced-apart, parallel rows of magnets extending along the length of the cathode body. The rows usually are arranged with outermost rows near the edge of the target material, the outermost rows providing a south magnetic pole. The outermost rows are joined at each end thereof by shorter rows of magnets also providing a south magnetic pole. An innermost row is generally located equidistant from the outermost rows and provides a north pole. The rows of magnets are arranged on a ferro-magnetic magnet-backing plate or flux-return plate.
The above-described magnet-array provides a magnetic field having the form of a continuous tunnel extending in an elongated loop over the target material. This field defines a sputtering zone on the surface of the target material. Sputtering occurs primarily in this sputtering zone with the result that the target material is preferentially eroded in this zone to provide an erosion-zone having the form of the magnetic field. This erosion-zone is generally referred to by sputtering practitioners as the "racetrack" because of its characteristic form.
The above-described linear planar-magnetron has certain well known disadvantages, for example, as sputtering occurs primarily in the racetrack, target material may be completely eroded in the racetrack area before significant erosion has occurred elsewhere on the target material. Because of this, target material must be replaced after only a relatively small fraction of it, generally between about twenty-five and thirty-five percent, has been sputtered. Additionally, concentration of sputtering in the racetrack area concentrates generation of heat in this area. This eventually limits the power at which the linear planar-magnetron can be operated and thus limits the rate at which material can be sputtered.
Another disadvantage of the above-described linear planar-magnetron is found when it is used to deposit insulating materials by DC reactive-sputtering, particularly when it is used to deposit silicon dioxide by DC reactively sputtering silicon in an atmosphere including oxygen. When depositing an insulating material, the material is deposited on the surface of the target outside the racetrack area and builds an insulating layer on the surface of the target material. The insulating layer causes charge build-up on the surface of the target material which frequently is discharged in the form of an arc. Such an arc destabilizes sputtering conditions and may cause debris resulting from the arc to be deposited on a substrate being coated.
Solutions to preferential sputtering of a planar-magnetron target have been proposed. Certain of these solutions involve relative motion between the magnet-array and the target material.
McKelvey in U.S. Pat. No. 4,422,916 describes a linear magnetron having a cylindrical cathode body including a layer of target material on the outer surface of the body. Water may be passed through the body for cooling the magnetron during sputtering. A magnet-array within the body extends along the length of the body and defines a narrow elongated sputtering zone over the target material. The cylindrical body may be rotated continuously over the magnet-array during sputtering, with the result that almost the entire surface of the target material is sputtered.
The McKelvey magnetron is generally referred to as a rotating cylindrical-magnetron. A rotating cylindrical-magnetron similar to the McKelvey magnetron is available commercially, under the trade name "C-Mag", from Airco Coating Technologies of Fairfield, Calif.
The rotating cylindrical-magnetron substantially overcomes the preferential target sputtering disadvantage of the linear planar-magnetron, however it has it is often difficult to apply target material to the surface of the cylindrical cathode body. This true in the case of a material such as silicon which can not be readily fabricated in the form of a tube. Silicon material can be applied to a cylindrical cathode body by plasma spraying powdered silicon onto the cathode body, the resulting silicon layer however is porous. A porous layer may, at least partially, disintegrate during sputtering. Such disintegration may lead, for example, to reduction of target life.
Corbani, in German Offenlegungsschrift DE 27 07 144, describes, in principle, several magnetron arrangements including relative motion between a magnet-array and a sputtering-target. The Corbani patent is directed primarily to planar-magnetron and non-planar-magnetron arrangements in which the magnet-array is significantly smaller than the target surface area. In each of the arrangements, the magnet-array is moved about the target surface area such that the whole surface may eventually be evenly sputtered, it is evident, however, that for depositing films on a large surface area these arrangements would provide only a relatively low deposition rate.
A linear planar-magnetron cathode including a moving magnet is not believed to be commercially available. In large scale in-line sputtering machines of the type used for coating architectural glazings, the magnetrons used are either fixed-magnet-array planar-magnetrons or McKelvey type rotating cylindrical-magnetrons.
A linear planar-magnetron including a moving magnet-array would be particularly advantageous for depositing silicon dioxide films at a high rate by sputtering silicon in an atmosphere including oxygen. Silicon target material could be applied to the target backing plate in the form of tiles of crystalline silicon material, and the entire area of the silicon target material could be sputtered, thus significantly reducing the arcing problem encountered when sputtering silicon using a conventional planar-magnetron. Such a device would provide the advantages of a rotating cylindrical magnetron without the disadvantage presented by a porous silicon target material
A significant problem in the design of a practical moving-magnet planar-magnetron is that, for reasons of preserving reliability of bearings and seals associated with magnet-moving apparatus, the magnet-array should not located in an enclosure including cooling-water. Cooling must thus be applied within the target backing plate. A target backing plate, however, is limited in thickness, because the magnet-array must be held relatively close to the target material to provide an optimum field shape. Providing effective means for target-cooling is thus very important in developing a reliable high-deposition-rate moving-magnet linear planar-magnetron for large scale in-line sputtering apparatus.